484 lines
13 KiB
Plaintext
484 lines
13 KiB
Plaintext
=========================================
|
|
How to get printk format specifiers right
|
|
=========================================
|
|
|
|
:Author: Randy Dunlap <rdunlap@infradead.org>
|
|
:Author: Andrew Murray <amurray@mpc-data.co.uk>
|
|
|
|
Integer types
|
|
=============
|
|
|
|
::
|
|
|
|
If variable is of Type, use printk format specifier:
|
|
------------------------------------------------------------
|
|
int %d or %x
|
|
unsigned int %u or %x
|
|
long %ld or %lx
|
|
unsigned long %lu or %lx
|
|
long long %lld or %llx
|
|
unsigned long long %llu or %llx
|
|
size_t %zu or %zx
|
|
ssize_t %zd or %zx
|
|
s32 %d or %x
|
|
u32 %u or %x
|
|
s64 %lld or %llx
|
|
u64 %llu or %llx
|
|
|
|
If <type> is dependent on a config option for its size (e.g., ``sector_t``,
|
|
``blkcnt_t``) or is architecture-dependent for its size (e.g., ``tcflag_t``),
|
|
use a format specifier of its largest possible type and explicitly cast to it.
|
|
|
|
Example::
|
|
|
|
printk("test: sector number/total blocks: %llu/%llu\n",
|
|
(unsigned long long)sector, (unsigned long long)blockcount);
|
|
|
|
Reminder: ``sizeof()`` result is of type ``size_t``.
|
|
|
|
The kernel's printf does not support ``%n``. For obvious reasons, floating
|
|
point formats (``%e, %f, %g, %a``) are also not recognized. Use of any
|
|
unsupported specifier or length qualifier results in a WARN and early
|
|
return from vsnprintf.
|
|
|
|
Raw pointer value SHOULD be printed with %p. The kernel supports
|
|
the following extended format specifiers for pointer types:
|
|
|
|
Pointer Types
|
|
=============
|
|
|
|
Pointers printed without a specifier extension (i.e unadorned %p) are
|
|
hashed to give a unique identifier without leaking kernel addresses to user
|
|
space. On 64 bit machines the first 32 bits are zeroed. If you _really_
|
|
want the address see %px below.
|
|
|
|
::
|
|
|
|
%p abcdef12 or 00000000abcdef12
|
|
|
|
Symbols/Function Pointers
|
|
=========================
|
|
|
|
::
|
|
|
|
%pF versatile_init+0x0/0x110
|
|
%pf versatile_init
|
|
%pS versatile_init+0x0/0x110
|
|
%pSR versatile_init+0x9/0x110
|
|
(with __builtin_extract_return_addr() translation)
|
|
%ps versatile_init
|
|
%pB prev_fn_of_versatile_init+0x88/0x88
|
|
|
|
The ``F`` and ``f`` specifiers are for printing function pointers,
|
|
for example, f->func, &gettimeofday. They have the same result as
|
|
``S`` and ``s`` specifiers. But they do an extra conversion on
|
|
ia64, ppc64 and parisc64 architectures where the function pointers
|
|
are actually function descriptors.
|
|
|
|
The ``S`` and ``s`` specifiers can be used for printing symbols
|
|
from direct addresses, for example, __builtin_return_address(0),
|
|
(void *)regs->ip. They result in the symbol name with (``S``) or
|
|
without (``s``) offsets. If KALLSYMS are disabled then the symbol
|
|
address is printed instead.
|
|
|
|
The ``B`` specifier results in the symbol name with offsets and should be
|
|
used when printing stack backtraces. The specifier takes into
|
|
consideration the effect of compiler optimisations which may occur
|
|
when tail-call``s are used and marked with the noreturn GCC attribute.
|
|
|
|
Examples::
|
|
|
|
printk("Going to call: %pF\n", gettimeofday);
|
|
printk("Going to call: %pF\n", p->func);
|
|
printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
|
|
printk("%s: called from %pS\n", __func__,
|
|
(void *)__builtin_return_address(0));
|
|
printk("Faulted at %pS\n", (void *)regs->ip);
|
|
printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
|
|
|
|
Kernel Pointers
|
|
===============
|
|
|
|
::
|
|
|
|
%pK 01234567 or 0123456789abcdef
|
|
|
|
For printing kernel pointers which should be hidden from unprivileged
|
|
users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see
|
|
Documentation/sysctl/kernel.txt for more details.
|
|
|
|
Unmodified Addresses
|
|
====================
|
|
|
|
::
|
|
|
|
%px 01234567 or 0123456789abcdef
|
|
|
|
For printing pointers when you _really_ want to print the address. Please
|
|
consider whether or not you are leaking sensitive information about the
|
|
Kernel layout in memory before printing pointers with %px. %px is
|
|
functionally equivalent to %lx. %px is preferred to %lx because it is more
|
|
uniquely grep'able. If, in the future, we need to modify the way the Kernel
|
|
handles printing pointers it will be nice to be able to find the call
|
|
sites.
|
|
|
|
Struct Resources
|
|
================
|
|
|
|
::
|
|
|
|
%pr [mem 0x60000000-0x6fffffff flags 0x2200] or
|
|
[mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
|
|
%pR [mem 0x60000000-0x6fffffff pref] or
|
|
[mem 0x0000000060000000-0x000000006fffffff pref]
|
|
|
|
For printing struct resources. The ``R`` and ``r`` specifiers result in a
|
|
printed resource with (``R``) or without (``r``) a decoded flags member.
|
|
Passed by reference.
|
|
|
|
Physical addresses types ``phys_addr_t``
|
|
========================================
|
|
|
|
::
|
|
|
|
%pa[p] 0x01234567 or 0x0123456789abcdef
|
|
|
|
For printing a ``phys_addr_t`` type (and its derivatives, such as
|
|
``resource_size_t``) which can vary based on build options, regardless of
|
|
the width of the CPU data path. Passed by reference.
|
|
|
|
DMA addresses types ``dma_addr_t``
|
|
==================================
|
|
|
|
::
|
|
|
|
%pad 0x01234567 or 0x0123456789abcdef
|
|
|
|
For printing a ``dma_addr_t`` type which can vary based on build options,
|
|
regardless of the width of the CPU data path. Passed by reference.
|
|
|
|
Raw buffer as an escaped string
|
|
===============================
|
|
|
|
::
|
|
|
|
%*pE[achnops]
|
|
|
|
For printing raw buffer as an escaped string. For the following buffer::
|
|
|
|
1b 62 20 5c 43 07 22 90 0d 5d
|
|
|
|
few examples show how the conversion would be done (the result string
|
|
without surrounding quotes)::
|
|
|
|
%*pE "\eb \C\a"\220\r]"
|
|
%*pEhp "\x1bb \C\x07"\x90\x0d]"
|
|
%*pEa "\e\142\040\\\103\a\042\220\r\135"
|
|
|
|
The conversion rules are applied according to an optional combination
|
|
of flags (see :c:func:`string_escape_mem` kernel documentation for the
|
|
details):
|
|
|
|
- ``a`` - ESCAPE_ANY
|
|
- ``c`` - ESCAPE_SPECIAL
|
|
- ``h`` - ESCAPE_HEX
|
|
- ``n`` - ESCAPE_NULL
|
|
- ``o`` - ESCAPE_OCTAL
|
|
- ``p`` - ESCAPE_NP
|
|
- ``s`` - ESCAPE_SPACE
|
|
|
|
By default ESCAPE_ANY_NP is used.
|
|
|
|
ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
|
|
printing SSIDs.
|
|
|
|
If field width is omitted the 1 byte only will be escaped.
|
|
|
|
Raw buffer as a hex string
|
|
==========================
|
|
|
|
::
|
|
|
|
%*ph 00 01 02 ... 3f
|
|
%*phC 00:01:02: ... :3f
|
|
%*phD 00-01-02- ... -3f
|
|
%*phN 000102 ... 3f
|
|
|
|
For printing a small buffers (up to 64 bytes long) as a hex string with
|
|
certain separator. For the larger buffers consider to use
|
|
:c:func:`print_hex_dump`.
|
|
|
|
MAC/FDDI addresses
|
|
==================
|
|
|
|
::
|
|
|
|
%pM 00:01:02:03:04:05
|
|
%pMR 05:04:03:02:01:00
|
|
%pMF 00-01-02-03-04-05
|
|
%pm 000102030405
|
|
%pmR 050403020100
|
|
|
|
For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
|
|
specifiers result in a printed address with (``M``) or without (``m``) byte
|
|
separators. The default byte separator is the colon (``:``).
|
|
|
|
Where FDDI addresses are concerned the ``F`` specifier can be used after
|
|
the ``M`` specifier to use dash (``-``) separators instead of the default
|
|
separator.
|
|
|
|
For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
|
|
specifier to use reversed byte order suitable for visual interpretation
|
|
of Bluetooth addresses which are in the little endian order.
|
|
|
|
Passed by reference.
|
|
|
|
IPv4 addresses
|
|
==============
|
|
|
|
::
|
|
|
|
%pI4 1.2.3.4
|
|
%pi4 001.002.003.004
|
|
%p[Ii]4[hnbl]
|
|
|
|
For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
|
|
specifiers result in a printed address with (``i4``) or without (``I4``)
|
|
leading zeros.
|
|
|
|
The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
|
|
host, network, big or little endian order addresses respectively. Where
|
|
no specifier is provided the default network/big endian order is used.
|
|
|
|
Passed by reference.
|
|
|
|
IPv6 addresses
|
|
==============
|
|
|
|
::
|
|
|
|
%pI6 0001:0002:0003:0004:0005:0006:0007:0008
|
|
%pi6 00010002000300040005000600070008
|
|
%pI6c 1:2:3:4:5:6:7:8
|
|
|
|
For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
|
|
specifiers result in a printed address with (``I6``) or without (``i6``)
|
|
colon-separators. Leading zeros are always used.
|
|
|
|
The additional ``c`` specifier can be used with the ``I`` specifier to
|
|
print a compressed IPv6 address as described by
|
|
http://tools.ietf.org/html/rfc5952
|
|
|
|
Passed by reference.
|
|
|
|
IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
|
|
=========================================================
|
|
|
|
::
|
|
|
|
%pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
|
|
%piS 001.002.003.004 or 00010002000300040005000600070008
|
|
%pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
|
|
%pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
|
|
%p[Ii]S[pfschnbl]
|
|
|
|
For printing an IP address without the need to distinguish whether it``s
|
|
of type AF_INET or AF_INET6, a pointer to a valid ``struct sockaddr``,
|
|
specified through ``IS`` or ``iS``, can be passed to this format specifier.
|
|
|
|
The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
|
|
(IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
|
|
flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
|
|
|
|
In case of an IPv6 address the compressed IPv6 address as described by
|
|
http://tools.ietf.org/html/rfc5952 is being used if the additional
|
|
specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
|
|
case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
|
|
https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
|
|
|
|
In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
|
|
specifiers can be used as well and are ignored in case of an IPv6
|
|
address.
|
|
|
|
Passed by reference.
|
|
|
|
Further examples::
|
|
|
|
%pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
|
|
%pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
|
|
%pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
|
|
|
|
UUID/GUID addresses
|
|
===================
|
|
|
|
::
|
|
|
|
%pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
|
|
%pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
|
|
%pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
|
|
%pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
|
|
|
|
For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
|
|
'b' and 'B' specifiers are used to specify a little endian order in
|
|
lower ('l') or upper case ('L') hex characters - and big endian order
|
|
in lower ('b') or upper case ('B') hex characters.
|
|
|
|
Where no additional specifiers are used the default big endian
|
|
order with lower case hex characters will be printed.
|
|
|
|
Passed by reference.
|
|
|
|
dentry names
|
|
============
|
|
|
|
::
|
|
|
|
%pd{,2,3,4}
|
|
%pD{,2,3,4}
|
|
|
|
For printing dentry name; if we race with :c:func:`d_move`, the name might be
|
|
a mix of old and new ones, but it won't oops. ``%pd`` dentry is a safer
|
|
equivalent of ``%s`` ``dentry->d_name.name`` we used to use, ``%pd<n>`` prints
|
|
``n`` last components. ``%pD`` does the same thing for struct file.
|
|
|
|
Passed by reference.
|
|
|
|
block_device names
|
|
==================
|
|
|
|
::
|
|
|
|
%pg sda, sda1 or loop0p1
|
|
|
|
For printing name of block_device pointers.
|
|
|
|
struct va_format
|
|
================
|
|
|
|
::
|
|
|
|
%pV
|
|
|
|
For printing struct va_format structures. These contain a format string
|
|
and va_list as follows::
|
|
|
|
struct va_format {
|
|
const char *fmt;
|
|
va_list *va;
|
|
};
|
|
|
|
Implements a "recursive vsnprintf".
|
|
|
|
Do not use this feature without some mechanism to verify the
|
|
correctness of the format string and va_list arguments.
|
|
|
|
Passed by reference.
|
|
|
|
kobjects
|
|
========
|
|
|
|
::
|
|
|
|
%pO
|
|
|
|
Base specifier for kobject based structs. Must be followed with
|
|
character for specific type of kobject as listed below:
|
|
|
|
Device tree nodes:
|
|
|
|
%pOF[fnpPcCF]
|
|
|
|
For printing device tree nodes. The optional arguments are:
|
|
f device node full_name
|
|
n device node name
|
|
p device node phandle
|
|
P device node path spec (name + @unit)
|
|
F device node flags
|
|
c major compatible string
|
|
C full compatible string
|
|
Without any arguments prints full_name (same as %pOFf)
|
|
The separator when using multiple arguments is ':'
|
|
|
|
Examples:
|
|
|
|
%pOF /foo/bar@0 - Node full name
|
|
%pOFf /foo/bar@0 - Same as above
|
|
%pOFfp /foo/bar@0:10 - Node full name + phandle
|
|
%pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
|
|
major compatible string +
|
|
node flags
|
|
D - dynamic
|
|
d - detached
|
|
P - Populated
|
|
B - Populated bus
|
|
|
|
Passed by reference.
|
|
|
|
|
|
struct clk
|
|
==========
|
|
|
|
::
|
|
|
|
%pC pll1
|
|
%pCn pll1
|
|
%pCr 1560000000
|
|
|
|
For printing struct clk structures. ``%pC`` and ``%pCn`` print the name
|
|
(Common Clock Framework) or address (legacy clock framework) of the
|
|
structure; ``%pCr`` prints the current clock rate.
|
|
|
|
Passed by reference.
|
|
|
|
bitmap and its derivatives such as cpumask and nodemask
|
|
=======================================================
|
|
|
|
::
|
|
|
|
%*pb 0779
|
|
%*pbl 0,3-6,8-10
|
|
|
|
For printing bitmap and its derivatives such as cpumask and nodemask,
|
|
``%*pb`` output the bitmap with field width as the number of bits and ``%*pbl``
|
|
output the bitmap as range list with field width as the number of bits.
|
|
|
|
Passed by reference.
|
|
|
|
Flags bitfields such as page flags, gfp_flags
|
|
=============================================
|
|
|
|
::
|
|
|
|
%pGp referenced|uptodate|lru|active|private
|
|
%pGg GFP_USER|GFP_DMA32|GFP_NOWARN
|
|
%pGv read|exec|mayread|maywrite|mayexec|denywrite
|
|
|
|
For printing flags bitfields as a collection of symbolic constants that
|
|
would construct the value. The type of flags is given by the third
|
|
character. Currently supported are [p]age flags, [v]ma_flags (both
|
|
expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
|
|
names and print order depends on the particular type.
|
|
|
|
Note that this format should not be used directly in :c:func:`TP_printk()` part
|
|
of a tracepoint. Instead, use the ``show_*_flags()`` functions from
|
|
<trace/events/mmflags.h>.
|
|
|
|
Passed by reference.
|
|
|
|
Network device features
|
|
=======================
|
|
|
|
::
|
|
|
|
%pNF 0x000000000000c000
|
|
|
|
For printing netdev_features_t.
|
|
|
|
Passed by reference.
|
|
|
|
If you add other ``%p`` extensions, please extend lib/test_printf.c with
|
|
one or more test cases, if at all feasible.
|
|
|
|
|
|
Thank you for your cooperation and attention.
|